For the compensation of carrier-frequency fluctuations due to changes in ambient temperature it is customary to use a resistance network including one or more thermistors disposed in the vicinity of the oscillator so as to sense the temperature changes affecting the quartz crystal which acts as a frequency-controlling element thereof. A corrective voltage emitted by the resistance network is fed to an adjustable impedance, such as a varactor, in circuit with that crystal to counteract the thermal fluctuations in carrier frequency. For a reasonably precise compensation it is necessary to use relatively expensive thermistors with tolerance limits substantially less than those of ordinary thermistors whose resistances at a given temperature may deviate by as much as .+-.5% from the rated value.